1. Field of the Invention
The present invention relates to a method of preparing pattern data for combined use of two different exposure methods to a single resist so called to as xe2x80x9cintra-level mix and matchxe2x80x9d, and more particularly to a method of avoiding any disconnection due to misalignments or displacements between the two different exposure methods.
2. Description of the Related Art
The combined use of two different exposure methods to a single resist is so called to as xe2x80x9cintra-level mix and matchxe2x80x9d, wherein the two different exposure methods may be an electron beam exposure and a light beam exposure. The electron beam exposure is superior in resolving power, whilst the light beam exposure is superior in throughput. The electron beam exposure is carried out for forming fine patterns or small size patterns with high resolving power. The electron beam exposure is then carried out for forming remaining patterns with high throughput.
It is necessary for the xe2x80x9cintra-level mix and matchxe2x80x9d to provide an overlapping margin to at least one of two sets of the exposure pattern data for the light and electron beam exposures in consideration of an unavoidable displacement or misalignment of the exposure patterns. If no overlapping margin is provided to the two sets of the exposure pattern data, an unavoidable displacement or misalignment of the exposure patterns results in disconnection of the patterns.
A method of preparing exposure pattern data with any overlapping margin in the xe2x80x9cintra-level mix and matchxe2x80x9d is disclosed in xe2x80x9cMicroelectronic Engineeringxe2x80x9d vol. 27, pp. 231-234, which was published in 1995 from ELSEVIER, and entitled xe2x80x9cElectron beam/DUV intra-level mix-and-match lithography for random logic 0.25 xcexcm CMOSxe2x80x9d and reported by R. Jonckheere.
Fine patterns with a smaller size than 0.4 micrometers are formed by the electron beam exposure with the high resolving power and then the remaining patterns are formed by an KrF exposure with the high throughput. This xe2x80x9cintra-level mix and matchxe2x80x9d lithography is applied to form gate electrodes of the CMOS devices. On boundary regions between the KrF exposure patterns and the electron beam exposure pattern, the KrF exposure pattern has an overlapping margin which overlaps the electron beam exposure pattern by 0.1 micrometer.
The conventional method is to provide the overlapping margin to the electron beam exposure with the high throughput and low resolving power, wherein the overlapping margin makes the actual pattern size different from the designed size. The overlapping margin reduces the alignment margin to a base.
Japanese laid-open patent publication No. 11-204407 discloses another intra-level mix-and-match lithography, wherein fine patterns with smaller sizes than 0.25 micrometers are formed by the electron beam exposure and then the remaining patterns are formed by the KrF exposure, provided that the overlapping margin is provided to the electron beam exposure with the high resolving power. The intra-level mix-and-match lithography processes will be described hereafter.
FIG. 1 is a flow chart illustrative of a conventional intra-level mix-and-match lithography, provided that the overlapping margin is provided to the electron beam exposure with the high resolving power.
The preparation of the electron beam exposure pattern data will be described. In a first process PI, larger patterns than a predetermined reference size xe2x80x9cLthxe2x80x9d are extracted from pattern data D1 to prepare light pattern data D2 which will be converted to a reticule formation data for forming a reticule for the electron beam exposure.
The preparation of the electron beam exposure pattern data will subsequently be described. In a process P2, design pattern data D1 are modified to reduce pattern widths by xcex94W1 which is more than zero. In a process P3, a reference size is set to be Lthxe2x88x922xcex94W1, so that smaller patterns than the reference size of Lthxe2x88x922xcex94W1 are extracted to prepare electron beam exposure pattern bare data D3 which are free of any overlapping margin. In a process P4, the electron beam exposure pattern bare data D3 are modified to increase pattern widths by xcex94W2 which is more than zero, thereby preparing electron beam exposure pattern modified data D4 with overlapping margins. The electron beam exposure pattern modified data D4 are then converted into data for an electron beam writer.
FIGS. 2A through 2C are views of patterns in sequential processes for preparing electron beam exposure pattern data D4 with the overlapping margin. With reference to FIG. 2A, there are two different design patterns 1 and 2. The design pattern 1 has a minimum size L1 which is less than 2xcex94W1. The design pattern 2 has a minimum size L2 which is more than 2xcex94W1. The minimum sizes L1 and L2 are smaller than Lth which is the critical size for isolating the electron beam exposure pattern and the electron beam exposure pattern.
With reference to FIG. 2B, the design patterns 1 and 2 are modified to reduce the individual widths by xcex94W1. Slender stripe portions of the designed patterns 1 and 2 correspond to portions to be patterned by the electron beam exposure. Square shaped portions of the designed patterns 1 and 2 correspond to portions to be patterned by the light beam exposure. Since the minimum size L1 of the design pattern 1 is smaller than 2xcex94W1, then the slender stripe portion of the designed pattern 1 disappears, whilst the square shaped portions of the designed pattern 1 remain with size reductions. The slender stripe portion 7 and the square shaped portions 5 and 6 of the designed pattern 2 remain with size reductions, wherein the reference size is set to be Lthxe2x88x922xcex94W1. The slender stripe portion 7 is to be patterned by the electron beam exposure, whilst the square shaped portions 5 and 6 are to be patterned by the light beam exposure. The slender stripe portion 7 is free of any overlapping margin.
With reference to FIG. 2C, only the stripe portion 7 of the designed pattern 2 is increased in width by xcex94W2, to form an electron beam exposure pattern 8 having overlapping margins 9 and 10 with a size of xcex94W1+xcex94W2. If xcex94W1=xcex94W2, the size of the electron beam exposure pattern is not changed.
The electron beam exposure pattern data D4 with the overlapping margin are prepared from the designed pattern data D1. If the minimum size of the design pattern is not more than 2xcex94W1, then the above conventional method is not applicable because at least the minimum size part of the pattern disappears. It is possible that xcex94W1 is so set that 2xcex94W1 is not more than the critical size. In this case, however, the overlapping margin size is xcex94W1+xcex94W2, for which reasons it is difficult to obtain a sufficient overlapping margin. If xcex94W1 is size-reduced and xcex94W2 is size-increased, then it is possible to obtain a sufficient overlapping margin. In this case, however, the design size of the portion other than overlapping margin portion is changed.
In order to have solved the above problems, another countermeasure was proposed. FIG. 3 is a flow chart of another conventional exposure processes. This processes are disclosed in Japanese laid-open patent publication No. 11-204407. xcex94W1 is size-reduced, provided that the minimum-size portion of the pattern is not disappeared even allowing the disadvantage in size-reduction of the overlapping margin. However, a short side of the electron beam exposure pattern data is shifted by xcex94W3 in a process P5, in order to obtain the sufficient overlapping margin of xcex94W1+xcex94W2+xcex94W3. This method can not be implemented by the CAD system because the CAD system is incapable of shifting only the short sides of all the patterns.
The electron beam exposure pattern data are variable in long-side length. It is, actually, however, difficult to replacing the electron beam exposure pattern data into the modified pattern data having the overlapping margins.
The above conventional method has a further disadvantage that the following problem is raised if the electron beam exposure pattern is in contact directly with the light beam exposure pattern. FIG. 4A is a view of electron beam exposure patterns adjacent to light beam exposure patterns in sequential processes shown in FIG. 3. The original electron beam exposure pattern 11 is free of the overlapping margin to the light beam exposure patterns 12 and 13. After the processes P2 through P4 are carried out, then the original electron beam exposure pattern 11 is changed to a modified electron beam exposure pattern 14 with overlapping margins of xcex94W1+xcex94W2. The final electron beam exposure pattern 15 has overlapping margins of xcex94W1 +xcex94W2+xcex94W3.
FIG. 4B is a view of electron beam exposure patterns adjacent to light beam exposure patterns in sequential processes shown in FIG. 3. The original electron beam exposure pattern 16 is free of the overlapping margin. After the processes P2 through P4 are carried out, then the original electron beam exposure pattern 16 is changed to an electron beam exposure pattern 17 without overlapping margins. The final electron beam exposure pattern 18 has overlapping margins of xcex94W3, even the final electron beam exposure pattern 18 does not need any overlapping margins since the electron beam exposure pattern 16 is not adjacent to the light beam exposure pattern. This means that the electron beam exposure pattern, which is not adjacent to the light beam exposure pattern, is changed in size.
FIG. 5 is a view of two different type patterns, for example, first and second type patterns. The first type pattern 19 comprises two square-shaped light beam exposure pattern portions and a single slender stripe shape electron beam exposure pattern portion which connects the two square-shaped light beam exposure pattern portions, wherein one long side of the electron beam exposure pattern portion is aligned to one side of each of the two square-shaped light beam exposure pattern portions.
The second type pattern 20 comprises two square-shaped light beam exposure pattern portions and a single slender stripe shape electron beam exposure pattern portion which connects the two square-shaped light beam exposure pattern portions, wherein the electron beam exposure pattern portion is aligned to centers of the two square-shaped light beam exposure pattern portions.
FIG. 6 is a view of a position-shifted electron beam exposure pattern adjacent to light beam exposure patterns. If the electron beam exposure pattern is shifted by a smaller distance than the short side length of the electron beam exposure pattern, then the electron beam exposure pattern still overleaps the light beam exposure patterns. If the electron beam exposure pattern is shifted by a larger distance than the short side length of the electron beam exposure pattern, then the electron beam exposure pattern does not overleap the light beam exposure patterns. Namely, the pattern is disconnected. This problem is more serious if the short side length of the electron beam exposure pattern is small.
Consequently, the above described prior arts have the following disadvantages.
The first disadvantage is that it is difficult to add the overlap margin to the fine pattern. In accordance with the conventional method, the pattern width is reduced by xcex94W1 which is more than zero. If the pattern width is not more than 2xcex94W1, then the pattern width at least partially disappears. The CAD system is not applicable to shift the electron beam exposure pattern parts of the patterns without changing the pattern size.
The second disadvantage is that if the pattern data include the above first type pattern and if the shifted distance is larger than the minimum size or the short side length of the electron beam exposure pattern, then the pattern is disconnected.
In the above circumstances, the development of a novel method of preparing pattern data free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel method of preparing pattern data free from the above problems.
It is a further object of the present invention to provide a novel method of preparing pattern data with adding overlap margins between different pattern parts to be patterned in the different exposure methods without any change in the pattern size.
It is a still further object of the present invention to provide a novel preparing pattern data with adding overlap margins between different pattern parts to be patterned in the different exposure methods without any disconnection of the pattern.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.